First digital computer installed on a manned spacecraft goes to auction

A Space Age collectible that not only represents a first in space, but also a first in computer history is on the auction block in Dallas, Texas. As part of its Space Exploration Signature Auction, Heritage Auctions is taking bids for a vintage random access, non-destructive readout 4,096 bit memory plane that flew on Gemini 3. This ferric memory unit was an integral part of the Gemini Spacecraft Computer, which was the first computer installed in a manned space capsule.

The 4.25-in (10-cm) "memory chip" is set in a 4.75 x 4.75 x 0.5 in (12 x 12 x 1 cm) acrylic display. On this is a label reading, "One plane of RANAM (Random Access Non-Destructive Readout) Memory containing 4,096 bits of information. This memory orbited the earth in the Gemini mission, March 23, 1965."

The Gemini mission referred to is Gemini 3, which was the first manned flight of the Gemini program that flew for just 4 hours and 52 minutes in 1965. Launched from Cape Canaveral, Florida, with Commander Virgil "Gus" Grissom and Pilot John W. Young on board, it was a test flight of the two-man orbital capsule. It was the first manned spacecraft to maneuver and change orbit, and the only one to include a smuggled corn beef sandwich – which got the crew into a lot of trouble with NASA.

The on-board computer was necessary for complex maneuvers, such as the rendezvous of Gemini 6 and 7 in December 1965(Credit: NASA)

Installed in the Gemini 3 capsule, named Molly Brown, the Gemini Spacecraft Computer was built by IBM's Federal Systems Division, in Oswego, New York. Aside from its space firsts, it was also IBM's first completely silicon semiconductor computer, the first to use glass delay lines as registers, and the first airborne or spaceborne computer to use an auxiliary.

The reason why it was the first computer on a manned mission is that previous ones had little need of them. Soviet Vostok and Voskhod spacecraft were very simple ballistic spacecraft, as was the American Mercury capsule, which had only attitude controls and timed its re-entry retro fire by means of instructions from ground control. Gemini required a computer because it was designed to expand spaceflight capability and rehearse the maneuvers that would be needed for the Apollo Moon landings.

The digital serial computer was used as a backup guidance system during the ascent phase of liftoff, allowed the astronauts to make their own orbital calculations during orbital maneuvers, provided targeting guidance while rendezvousing with other spacecraft, and controlled the spacecraft's automatic re-entry.

Weighing 8.98 pounds (26.75 kg) and taking up 1.35 ft³ (3.82 l), the Gemini computer was tiny compared to many of its Earthbound counterparts. It was installed behind the pilot's instrument panel, which held the pushbutton and display devices that controlled it. In terms of architecture, it was very similar to the more advanced digital computer carried on the Apollo missions and used a similar interface. It was capable of 7,000 calculations a second, had a 500 kc bit rate, and a memory cycle time of 250 kc.

The memory plane on auction is a ferrite core memory, which was common in computers from about 1955 to 1975. It used tiny toroids or rings of magnetic iron threaded together with a crisscross pattern of electrical wires. These wires magnetized the rings and read the memory. Each ring represented one bit of memory and the magnetic direction indicated whether it was one or zero. With flexible instruction and data storage organization, it had a capacity of 4,096 bits or 512 bytes. According to NASA, the total memory of the computer was 20 KB. Because the magnetism persisted after the power was turned off, the ferric memory was regarded as non-volatile.

The auction includes the memory plane and a thirty-page technical document. It runs through November 3 and the current bid stands at US$2,000.